feat: add csharp solution to lc problem: No.0019

Author: djvelimir

solution/0000-0099/0019.Remove Nth Node From End of List/README.md

@@ -340,6 +340,37 @@ def remove_nth_from_end(head, n)
 end
 ```
 
+#### C#
+
+```cs
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public int val;
+ *     public ListNode next;
+ *     public ListNode(int val=0, ListNode next=null) {
+ *         this.val = val;
+ *         this.next = next;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode RemoveNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0, head);
+        ListNode fast = dummy, slow = dummy;
+        while (n-- > 0) {
+            fast = fast.next;
+        }
+        while (fast.next != null) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+        slow.next = slow.next.next;
+        return dummy.next;
+    }
+}
+```
+
 #### PHP
 
 ```php

solution/0000-0099/0019.Remove Nth Node From End of List/README_EN.md

@@ -337,6 +337,37 @@ def remove_nth_from_end(head, n)
 end
 ```
 
+#### C#
+
+```cs
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public int val;
+ *     public ListNode next;
+ *     public ListNode(int val=0, ListNode next=null) {
+ *         this.val = val;
+ *         this.next = next;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode RemoveNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0, head);
+        ListNode fast = dummy, slow = dummy;
+        while (n-- > 0) {
+            fast = fast.next;
+        }
+        while (fast.next != null) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+        slow.next = slow.next.next;
+        return dummy.next;
+    }
+}
+```
+
 #### PHP
 
 ```php

solution/0000-0099/0019.Remove Nth Node From End of List/Solution.cs

@@ -0,0 +1,26 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public int val;
+ *     public ListNode next;
+ *     public ListNode(int val=0, ListNode next=null) {
+ *         this.val = val;
+ *         this.next = next;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode RemoveNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0, head);
+        ListNode fast = dummy, slow = dummy;
+        while (n-- > 0) {
+            fast = fast.next;
+        }
+        while (fast.next != null) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+        slow.next = slow.next.next;
+        return dummy.next;
+    }
+}